Anhydrous ammonia NH3 although first known as a refrigerant, is the lowest cost source of nitrogen for use as a fertilizer for fertilizing crops. Anhydrous ammonia NH3 is made from natural gas and air, and is 82% nitrogen and 18% hydrogen by weight. Although anhydrous ammonia has a foul odor and is hazardous as an inhalant, it is a very popular fertilizer for use on row crops. For transport and storage, anhydrous ammonia is compressed so that it is a liquid at atmospheric temperatures. During application to fields for fertilizing row crops the anhydrous ammonia stored as liquid is expanded into a gas and injected into soil.
The typical electronically-controlled ammonia application system consists of a nurse tank trailed behind a tool bar which is attached to a tractor. A computer console is mounted accessible to the tractor operator. The typical mechanical ammonia application system is about the same as the electronic system, however it utilizes a manually-adjustable mechanical meter. The nurse tank is a trailer-mounted pressure vessel which contains the ammonia in its liquid state. A liquid withdrawal valve is mounted at the top of the tank and has a dip tube which extends to the bottom of the tank to withdraw the ammonia in liquid form. A suitable hose connects this valve to a filter connected to a main shutoff valve mounted on the tool bar. The ammonia then flows through a heat exchanger unit, then through a meter, then to an electronically controlled throttling valve, then to one or more dividing manifolds, and finally through suitable hoses to a applicator knives which inject the ammonia into the soil. As the liquid ammonia enters the dip tube located at the bottom of the tank and begins to flow, its thermodynamic conditions begin to change. The ammonia begins to expand. This results in the formation of ammonia vapor within the system which must be removed by a heat exchanger unit prior to metering in order to assure a properly-measured quantity of ammonia to the applicator knives and into the soil. These systems work fairly well, but under certain conditions problems can arise. The greater expansion of the ammonia across the total system often forms more vapor than the typical heat exchanger unit can handle.
Often various types of electronics including GPS are used to assure that fertilizers are spread evenly across a field. However, over the last sixty years of using anhydrous ammonia injecting into the ground of a field, the accuracy is usually the best up to 10% in so far as assuring that the anhydrous ammonia is equally distributed across the various rows in a field. Unequal distribution of anhydrous ammonia in a field may often be observed by comparing the height of adjacent rows of crops, which have been observed to vary as much as two feet.
The anhydrous ammonia is metered to apply selected amounts for different crops, such as corn requires more than twice the amount of ammonia per acre than the smaller grain crops. Problems often occur in metering ammonia since nitrogen expands in going from a liquid to a gas, often changing in volume in a ratio of one to eight hundred. Anhydrous ammonia is also a very good refrigerant and its temperatures are reduced as it expends from a liquid to gas. The metering problem is also exacerbated by the requirement of dividing the anhydrous nitrogen into equal flow streams to allow equal distribution of the nitrogen along the tool bars for a conventional row crop injection systems. The tool bars are typically seventy feet long and are pull behind a tractor, transverse to crop rows. The applicator knives are mounted to the tool bars for running about two inches into the ground and depositing nitrogen into the soil. The anhydrous nitrogen moving to the tool bar is a flowing mixture of decreasing liquid, and increasing and expanding vapor which requires dividing into equal amounts for passing to the various applicator knives spaced apart along the length of the tool bar. Dividing anhydrous nitrogen into equal flow streams is also made more difficult by the flow of the liquid and vapor phases separating into different slip stream flows, which is not a homogenous mixture.